Cooking utensils are in use, which during operation are covered with a relatively tightly closing lid, so that when the heat supply to such a cooking utensil drops and the food cools off, an underpressure is formed inside of said cooking utensil and thus the cooking process of the food continues in an accelerated manner. Of course, care must be taken that the atmospheric pressure on the lid remains limited and that same cannot be deformed or even destroyed. Moreover, the possibility of bringing about a pressure balance relative to the outside must exist at any time in order to be able to remove the lid without any problems from the cooking utensil. A suitable safety and vent valve must therefore be provided in the cooking utensil.
It is already known, and it is also obvious, to equip such a valve with a valve spring, by the force of which spring a valve plate is loaded such that it rests on a valve seat and prevents, during normal operation, a pressure balance between the inside of the cooking utensil and the outside. The valve spring is increasingly loaded upon an increase in the underpressure until at an adjusted limit value it opens the valve and relieves the underpressure through the lid. Moreover a central, hand-operated pressure knob is integrated into the knoblike valve member, which as a rule is connected to the lid by means of a fastening thread, with which pressure knob the valve can be opened without any consideration of the accumulated underpressure.
Such a valve is rather complicated because the pressure knob must be mounted axially and limited with a screw connection. It is particularly disadvantageous that the valve can become dirty in the area of the valve spring constructed as a coil spring and its preadjusted spring force is thereby changed so that an automatic opening of the valve will no longer occur at the originally adjusted underpressure. Fastening of the valve member on the lid demands an additional work for sealing and holding a flange or the like fastened on the lid, into which the valve member can be screwed.